1. Field of the Invention
The present invention is related to receivers of the type which are employed in digital data computer systems. More particularly, the present receiver is adapted to receive weak digital signals in the form of light from fiber-optic waveguides and to process the signals into digital data usable by the computer system and its peripheral equipment. The receiver detects the weak signals and highly amplifies the signals in a manner which ordinarily introduces distortion. Processing circuits are employed to process the distorted amplified signals and to generate a data output representative of the original data signals employed to generate the light signals.
2. Description of the Prior Art
Fiber-optic waveguides are commercially available and are being used as a substitute or replacement for conventional coaxial cables. Fiber-optic waveguides have the disadvantage of transmitting less energy than conventional coaxial cables and the attenuation over a substantial length is much higher than conventional cables. Accordingly, the light energy being received must be detected and highly amplified to be usable in most digital data computing systems.
Typical applications of fiber-optic waveguides are found in the connection between the central processing unit and the associated auxiliary or peripheral equipment in a computing system. In such applications both the central processing unit and the peripheral equipment are operated with digital data signals generally described as square wave pulses presented in coded form. The original digital data in coded form is employed to activate a light generator such as a light emitting diode (LED) which supplies light to one end of the waveguide. A detector, such as an optical diode, receives the light at the other end of the fiber-optic waveguide and generates a weak signal. The weak signal from the optical diode is then amplified and processed to provide a digital data output representative of the original coded digital data which was employed to activate the light generator.
The circuits which receive the light signals, detect, amplify and process the light signals are referred to hereinafter as optical receivers. Optical receivers are known and are in commercial use. Heretofore, optical receivers have highly amplified detected light signals and fed them to a comparator having a reference voltage input. This type of prior art optical receiver introduced problems of pulse width, distortion and usually required an optical receiver having a much higher band width than the frequency of the original digital data. In order to reduce the distortion of the digital data signals in the prior art processing system, the optical receivers were modified or the optical receivers were adapted to use coded systems which had only a fifty percent duty cycle. It is known that coding systems having a fifty percent duty cycle are not representative of coding systems which are capable of the highest frequency and highest density presently being employed in high speed computing systems.
In another form of prior art optical receiver, the output signals from the preamplifier are differentiated and then fed to a flip-flop circuit which generates a square wave output. A prior art system of this type is designed to eliminate the distortions due to the floating A.C. voltage signals, however, this system introduces the problem of responding to noise signals as well as usually requiring a higher band width receiver.
When digital data signals are transmitted at high speeds, the prior art receivers tend to delay and distort the digital data signals, most of the prior art optical receivers have heretofore required at least twice the band width of the digital data signal system.